Development of the Tree and Stand Simulator (TASS) Version 3.0.

This technical report details the evolution and mechanics of the Tree and Stand Simulator, a spatially explicit individual tree model used to forecast forest growth and timber yield in British Columbia. The rimary purpose of this report is to introduce TASS III, a third-generation version designed to simulate mixed-species and multi-cohort stands with greater biological realism. Central to this advancement is the integration of a light dispersion model that governs how individual tree crowns interact, compete for resources, and respond to shading across different canopy layers. By refining algorithms for height growth, branch extension, and mortality, and introducing a user-friendly graphical interface, the report provides foresters with a robust tool for evaluating complex silviculture scenarios and long-term forest resiliency.